In the taking of plankton samples from a body of water it is conventional to secure the smaller end of a conical net to the open end of a sample container and move the assembled net and container through the body of water. Apparatus of this kind is disclosed in Phillips Pat. No. 4,089,131. Although the apparatus disclosed in that patent is satisfactory, extensive use of such apparatus has revealed the desirability of improvements. For example, the patented apparatus uses a container having a relatively small neck. The passage of samples into and out of the container and cleaning of the latter are easier if the relatively small neck container is replaced by a wide-mouth container.
Although the apparatus disclosed in the Phillips patent is capable of effecting an excellent seal between the container and the coupling by means of which the container is coupled to the plankton net, it is possible for plankton to become wedged between the external surface of the container neck and the innermost part of the coupling. This possibility is increased in the event that the container and coupling are carelessly assembled or in the event that towing of the apparatus through a body of water causes relative rotation with consequent looseness between the container and the coupling. This problem can be solved by the provision of a sealing bead on the coupling which is accommodated in the mouth of the container and by providing a latch for preventing unintentional relative rotation between the container and the coupling.